1. Field of the Invention
The present invention relates to a Continuously Variable Transmission (CVT) belt inspection method and associated CVT belt inspection device. More particularly, the present invention relates to a CVT belt inspection method and CVT belt inspection device designed for a large number of stacked layer metal elements punched and processed into a specified shape which are assembled to support two laminated bands of a metal stepless belt (hereinafter denoted as “metal belt”).
2. Description of the Related Art
FIGS. 7A˜7B are outline views of a CVT belt disclosed in Japanese Laid-Open (Kokai) Patent Application No. 2001-21007 titled “BELT FOR CONTINUOUSLY VARIABLE TRANSMISSION”, etc. In this diagram, a CVT belt 1 is constructed by assembling two laminated belts 2 containing a plurality of metal belts 2a (for example, a stack of about 12 endless layers) which are supported by thin trapezoidal layered elements 3 composed of a large number of metal elements 3a (for example, about 400 consecutive elements).
Each of the metal elements 3a consists of a steel block (small piece of metal) punched and processed from a metal plate and molded into a specified shape, for example, the physical form resembling the upper-half image of a human body. Specifically, a metal element 3a resembles a molded shape having a head portion 3b and a chest portion 3c, along with a neck portion 3d which connects between the head portion 3b and the chest portion 3c. 
The head portion 3b has a protrusion 3e (raised circular knurl) (front surface as seen in FIG. 7B) formed in one direction of the surface side and a cavity (circular indent) (rear surface not shown) formed in the same location on the opposite direction surface side. Alignment of the metal elements 3a is accomplished by consecutively inserting the protrusion 3e into the cavity of adjoining metal elements 3a. 
Two laminated belts 2 are inserted into the recessed parts 3f (belt grooves) formed between the head portion 3b and the chest portion 3c of the metal elements 3a, respectively. Here, when the gap (the space clearance width of the recessed parts 3f) between the head portion 3b and the chest portion 3c is defined as “L” (refer to FIG. 7B), the number of stacked layers for the laminated belts 2 is set so that the lamination thickness “D” for each of the laminated belts 2 (refer to FIG. 7A) becomes substantially “L” of an equivalent or slightly smaller value.
Apart from that, the CVT belt 1 is an essential torque transmission element for conveying driving force to a drive system in a vehicle, such as an automobile, etc. Especially, since sufficiently high tensile force is applied to the CVT belt 1 in a vehicle with a high-powered engine installed, the durability of the CVT belt 1 must be carefully considered.
Accordingly, the above-mentioned Japanese Patent Application No. 2001-21007 discloses the purpose as being effective by creating a shape for a particular part of the metal elements 3a in order to solve the above-mentioned limitation. This suggests the technological problem which has an adverse influence on the durability of the CVT belt 1 has been solved. Namely, this relates to the fatigue life of the metal belts 2a which becomes shortened due to friction and the combined push-pull action generated between the metal elements 3a and the metal belts 2a when applying torque transmission driving force.
Here, the “particular part” of the metal elements 3a is the part in contact with the metal belts 2a situated in the innermost circumference layer of the laminated belts 2. Specifically, the “particular part” of the metal elements 3a is both shoulder parts 3g of the chest portion 3c (hereinafter denoted as “element saddle part”) which experience powerful tensile and compressive forces when transmission driving force is applied.
The technical matter disclosed in the above-mentioned conventional prior art is applied when performing the forming process of the metal elements 3a exclusively. Hypothetically speaking, even if an ideal processing shape can be designed, it is still a paper plan. Namely, when components (metal elements 3a) are initially manufactured occurrences of “irregular shaped areas” are undeniable. For example, “burrs”, “collars”, “protrusions”, “swells” (bumps), etc. are common which are caused by punch processing deviation errors.
FIG. 8 is a diagram showing an irregular-shaped area example on a metal element 3a. In this drawing, a small protrusion 3h formed on the element saddle part 3g represents an irregular-shaped area. As also explained earlier, since this element saddle part 3g is the part pushed< >pulled by a strong force against the metal belts 2a situated in the innermost circumference layer of the laminated belts 2 when transmitting driving force, by the existence of this protrusion 3h, a flaw will be scarred on the surface of a metal belt 2a situated in the innermost circumference layer of the laminated belt 2. In addition, this flaw is observed as a glossy flaw, namely, a gloss mark. In this regard, the metal belt 2a surface constitutes a matted hardened coating (non-glossy lusterless finish) and the hardened coating is partly exfoliated by the protrusion 3h. As a result, the underlying base layer is exposed as being glossy. Also, an irregular-shaped area is not restricted to only the protrusion 3h in the diagram. Other abnormalities which can scrape away some of the metal belt 2a surface hardened layer such as an indentation, an adhered object, etc. are included.
The laminated belt 2 is only inserted in the recessed parts 3f of each of the metal elements 3a which constitute the layered elements 3. As both (the laminated belts 2 and the layered elements 3) have some relative displacement allowance in the circumferential direction of the ring when transmitting driving force, the above-mentioned flaw will be intermittent in the circumferential direction of a metal belt 2a and will cause a ring defect referred to as a “running track.”
As the conventional CVT belt inspection method and CVT belt inspection device of a CVT belt, for example, a CVT belt 1 is attached for a predetermined time interval to an actual vehicle (or attached to a testing device of an actual vehicle). After a trial use that exerts actual driving force, the CVT belt 1 is disassembled. The surface of the metal belt 2a situated in the innermost circumference layer of a laminated belt 2 is observed, and the method for judging the presence of the above-mentioned “running track” (a gloss mark which is intermittent in the circumferential direction) is considered. In this case, when judged as containing a running track, the related faulty metal elements 3a and the metal belt 2a with a “running track” are excluded as a defective product and the CVT belt 1 reassembled.
Apart from that, the cause which generates a “running track” is not only an irregular-shaped area of the metal elements 3a. For example, also a substance impurity (synonymous with contaminant), such as metal powder, etc., which enters the inner part of the CVT belt 1 can generate the above-mentioned flaw similar to a “running track,” namely, intermittent gloss marks.
Both types of flaws are common in regard to being intermittent gloss marks, and thus distinction of the cause is troublesome. For this reason, conventionally in cases where intermittent gloss marks are scarred on the metal belts 2a after trial use, the margin of safety is considered paramount. Thus, in those causes “deemed” irregular-shaped areas on the metal elements 3a, a total exchange of the metal elements 3a and replacement of the metal belts 2a is performed.
However, this is an excessive countermeasure and not preferred in terms of cost. A flaw attached by a substance impurity, such as metal powder, etc., creates simply a friction trace and the durability of a CVT belt 1 is not impaired.
Therefore, the present invention in relation to “running track” generation causes can at least patently distinguish between those generated due to a harmless substance impurity, such as metal powder, etc. as well those generated due a damaging irregular-shaped area. Particularly, the object of the present invention is to provide a CVT belt inspection method and a CVT belt inspection device which contribute significantly to cost reduction by not performing unnecessary part replacements in cases when distinguished as an innocuous impurity, such as metal powder, etc.